Missing env vars for plugin registry after loading a v1 devfile (was: Plugin registry became invalid after migration from 2.15 -> 3.0)

Steps to reproduce:

1st way:
1. Install DS 3.0
2. Use a factory to start the workspace with devfile v1: https://devspaces-url/#/https://raw.githubusercontent.com/redhat-developer/devspaces/crw-2.15-rhel-8/dependencies/che-devfile-registry/devfiles/05_cpp/devfile.yaml
3. Go to Plugins view by opening View --> Plugins
4. In the Plugins View we see 'your registry is invalid'
5. Open the terminal for theia-ide container and go to /devworkspace-metadata/
6. Open flattened.devworkspace.yaml file and see that theia-ide component doesn't have CHE_DASHBOARD_URL, CHE_PLUGIN_REGISTRY_URL and CHE_PLUGIN_REGISTRY_INTERNAL_URL environment variables.

2nd way:
1. install 2.15
2. migrate to 3.0
3. open vertx-health-checks-example-redhat project from sample tile in dashboard
4. right-click the pom.xml in the root of the project and run the Dependency Analytics command
4b. if not found, open View > Plugins and see if the plugin is installed / available.

5. Note the error 'your registry is invalid'

see more detailed notes / screenshots in https://issues.redhat.com/browse/CRW-2892?focusedCommentId=20203040&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-20203040